1. Field of the Invention
This invention relates to weapon systems.
More especially, though not exclusively, the invention is concerned with guidance and control systems for air-to-ground stand-off weapon systems.
2. Description of the Related Art
In many modern concepts such weapons systems, particularly for those intended for use against armoured formations and similarly dispersed targets, are conceived to consist of a guidable vehicle, which on being launched from an aircraft executes a trajectory to bring it to a suitable height and attitude above a target area either to itself attack a target, or to dispense a number of munitions for attacking targets, which munitions may themselves be terminally guided or not.
For example, in one such concept for a weapon system for use against armoured formations, the dispenser is unpowered, and contains eight terminally guided munitions. The dispenser is launched from the aircraft at low altitude. After release from the aircraft, the dispenser is first retarded to ensure that the launch aircraft can get clear, and then proceeds for a specified distance whilst maintaining as closely as possible the track angle which pertained at the time of release, in order to reach the target area. On approaching the target area, the dispenser executes a pull-up manoeuvre to achieve an altitude such that, when the munitions are released, their sensors will have a sufficient area within their collective field of view that there will be a good probability of acquiring many of the available targets. Having achieved such an altitude, the dispenser will place itself in a suitable attitude for releasing the munitions, and then eject them in an appropriate pattern. After ejection, each munition will continue in forward flight with its terminal sensor pointing downwards until the sensor acquires a target, whereupon the munition is guided down onto the target under the control of its sensor.
For such weapon systems, the guidance and control of the launched vehicle will normally impose a requirement for the measurement of its attitude, heading and angular rates. Likewise, in the case where the launched vehicle dispenses munitions which are terminally guided, there will normally be a requirement for the measurement of the angular orientation and angular rates of the munitions and/or their sensor heads. At the same time, the economic feasibility of the weapon system will require that all components of the weapon, particularly those replicated on each munition, be of low cost.
It is an object the present invention to provide a weapon system of the kind comprising a mobile platform incorporating an attitude reference sub-system and a guidable vehicle launchable from said platform and itself incorporating a guidance sub-system wherein the vehicle guidance sub-system may be of relatively low cost.
According to the present invention there is provided a weapon system comprising a mobile platform incorporating a first three-axis attitude reference sub-system; and a guidable vehicle launchable from the said platform and incorporating a guidance sub-system incorporating gyros; and wherein in operation of the system the attitude data of the platform and the vehicle are repetitively compared during a period of time before vehicle launch, being a period terminating substantially at the moment of launch of the vehicle from the platform, and at least one of the factors scale factor and zero offset currently being exhibited by each of the gyros of the vehicle guidance sub-system is estimated and a desired correction thereof effected using the differences in attitude data, as revealed by the said repetitive comparison, during a period of time terminating substantially at the said moment of vehicle launch.
In one particular weapon system according to the invention said vehicle is a munition dispenser, whose guidance sub-system incorporates a second three axis attitude reference sub-system, and which carries a multiplicity of guidable munitions launchable from the said dispenser and each incorporating a guidance and/or stabilisation sub-system incorporating gyros; and in operation of the system attitude data of the dispenser and each of the said munitions are repetitively compared during a period of time terminating substantially at the moment of launch of the relevant munition from the dispenser, and at least one of the factors scale factor and zero offset currently being exhibited by each of the gyros of each of the munition sub-systems is estimated and a desired correction thereof effected using the differences in attitude data, as revealed by the said repetitive comparison of attitude data of the dispenser and each of the said munitions, during a time period terminating substantially at the moment of launch of the relevant munition.
One advantage of the present invention arises from the fact that the correction of scale factor and/or zero offset of the gyros, i.e. in the dispenser and/or munitions guidance sub-systems, enables certain types of low-cost gyroscopes to be used in these sub-systems, e.g gyroscopes based on the vibrating element principle, wherein the stability of the gyro error parameters, particularly zero offset, over periods of operation of several minutes is very much better than their stability and repeatedly on a switch-on to switch-on basis, or in the face of large temperature variations. The poor stability and repeatability on a switch-on to switch-on basis and with large temperature variations of such gyros is overcome in a system according to the invention, and furthermore this is not negated by the possible severe manoeuvres and large attitude excursions to which the gyros may be subjected in operation.
A further feature of a system according to the invention is that if it may not be possible to satisfactorily estimate and correct the scale factor or zero offset of the gyro. Such an eventuality clearly prevents satisfactory operation of the system and can be used to provide a warning to the system operator that it may not be desirable to continue operation of the system, and that it may be desirable to abort the entire sortie rather than expose the platform, which may be a very costly aircraft, to danger in continuing with the sortie.
By a gyroscope based on the vibrating element principle is meant a gyroscope incorporating an element, normally in the form of a cylinder or disc, which is caused to vibrate in operation, the pattern of vibrations being caused to shift in response to angular movement about an axis of the element, the shift being detected to form the basis of the gyroscope output.